\( 2a - \frac{1}{3}b + 3a - \frac{2}{3}b = (2a + 3a) + \left(-\frac{1}{3}b - \frac{2}{3}b\right) = 5a + \left(-\frac{1+2}{3}\right)b = 5a - \frac{3}{3}b = 5a - b \).
Ответ: 5a - b.